Acidifying compound for photographic baths



Patented Apr. 10, 1951 ACIDIFYING COMPOUND FOR PHOTO- GRAPHIC BATHS No Drawing. Application October 4, 1947, Serial No. 778,035

3 Claims.

This invention relates to photographic compositions and particularly to an acidifying agent for photographic baths.

Certain photographic baths such as fixing baths require an acid material and it is desirable for packaging and storage purposes that the source of acid be a dry powder. The use of sodium acid sulfate as the principal acidifying agent in acid fixing baths and stop baths has been described by Crabtree, Muehler and Russell, Journal of the Society of Motion Picture Engineers, vol. 38, April 1942, page 353, and the use of alkali acid sulfates together with sodium acetate or similar salt for the preparation of photographic acid hardening fixing preparations in package form has been dicslosed by Russell and Muehler in U. S. Patent 2,378,248, granted June 12, 1945.

In packaging such materials, the moisture absorbing and retaining properties of sodium acid sulfate have been found to be suificient to cause caking of the mixtures when this component is mixed with highly hydrated salts such as the ordinary alums and kept for some time. Cardand paperboard containers are also readily attacked when such mixtures containing sodium acid sulfate are in contact with the paper under conditions of high humidity or in the presence of moisture from the hydrated salts.

It is, therefore, an object of the present invention to provide a novel dry solid acidifying agent for photographic baths. A further object is to provide a dry solid acidifying agent for photographic baths which is not subject to objectionable moisture absorption and caking. A still further object is to provide a dry photographic fixing composition not subject to caking or deliquescence. Other objects will appear from the following description of my invention.

These objects are accomplished by the use of potassium pyrosulfate as the acidifying agent in photographic powders for the preparation of photographic baths such as fixing baths.

I have found that potassium pyrosulf-ate is superior to the alkali acid sulfates and to fused sodium acid sulfate as a dry solid compound for use in prep ing photographic baths or packaged solid chemicals for the preparation of photographic baths. A satisfactory potassium pyrosulfate is represented by the product which has the formula K2S2O7 and has an acidity of 35% to 37% expressed as H2604.

Other satisfactory chemicals for use as herein disclosed are, for example, chemicals marketed with the designation potassium bisulfate, fused, in'both lump and powder forms, with acidity be- 2 tween 35 and 37% expressed as H2804. These appear to contain substantial amounts of potassium pyrosulfate (KzSzOw) together with various minor amounts of potassium sulfate and potassium acid sulfate (KI-I804). Such materials prepared by fusion or equivalent methods of dehydrating are also satisfactory since they consist essentially of potassium pyrosulfate. I also do not exclude and may use potassium bisulfate, fused, having acidity even somewhat below 35% expressed as H2804 since this is an example of a material containing a substantial amount of potassium pyrosulfate. Excess sulfuric acid (or $03) as an impurity in excess of that called for by the formula K2520": is generally undesirable,

particularly with paper containers, but may be tolerated in small amounts when packaging is done in glass or other corrosion resistant containers.

The potassium pyrosulfate of the present invention applies to a chemical comprising substantially potassium pyrosulfate (K2S2O7) which contains essentially no hydrogen and is differentiated from the previously disclosed alkali acid sulfates comprising sodium acid sulfate, also known as sodium hydrogen sulfate (WEI-I804) or sodium bisulfate (NaHSOi) sodium acid sulfate, anhydrous, or sodium bisulfate, fused; potassium acid sulfate (KHSOi) or potassium bisulfate (KI-ISO'4-I-I2O) which either contain hydrogen or readily form hydrates.

Potassium pyrosulfate is superior to the sodium acid sulfates for use alone or in addition to other substances for the preparation of photographic solutions or packaged powders for preparing photographic solutions such as acid fixing baths, acid hardening fixing baths, acid hardener solutions (for addition to thiosulfate solutions), acid stop baths, acid hardening stop baths, acid bleaching solutions for reversal processing or for halogenizing silver images and comprising oxidizing agents for silver such as potassium permanganate, alkali metal or ammonium bichromates, ferric, ceric or cupric sulfates or nitrates, or soluble chlorides or bromides, as well as for toning, intensifying and photographic image reducing solutions which contain acid ingredients.

I do not restrict the use of potassium pyrosulfate to the powdered form although this is the most readily soluble form of the compound.

The potassium pyrosulfate may be used'with buffer salts or with acids such as acetic, propionic, butyric, succinic, tartaric, citric and boric acid or may be used without buffer salts in case a strong acid is desired.

The potassium pyrosulfate may be used in any formula employing alkali acid sulfates and the equivalent weight required may be found by multiplying the weight of the alkali acid sulfate being replaced by the factor where n is the normality weight of the alkali acid sulfate. For water-free sodium acid sulfate (NaHSOi) with a normality weight of approximately 120, the factor is sufficiently near unity that for most practical purposes, an equal part of potassium pyrosulfate can be used.

The following examples illustrate my invention.

EXANLPLE 1 Chemicals for preparing acid. hardening firing bath Compartment A:

Grams Sodium thiosulfate, cryst. (hypo) 1 240 Sodium sulfite (desiccated) Sodium acetate (desiccated) 2O Compartment B:

Grams Boric acid crystals 7.5

Potassium alumflm; 15.0 Potassium pyrosulfate, fused, owder 30.0

Anhydrous sodium thiosulfate 150 grams may replace vthe crystalline hypo, if desired.

2 '(l1he boric acid may be placed in Compartment A if de- Sll'e For use: Dissolve the contents of Compartment A in approximately 500 cc. of water; then slowly add and dissolve with stirring the contents of Compartment B. Add water to make 1 liter.

To demonstrate the superiority of the potassium pyrosulfate, and intimate mixture of the chemicals as given in Example 1, Compartment B, was prepared. A similar sample was prepared but with substitution of an equal weight of fused powdered sodium acid sulfate for the pyrosulfate. When these samples were stored at elevated temperatures (for example, 110 F.) the sample containing potassium pyrosulfate remained dry indefinitely and could be poured or moved smoothly as a powder while that containing the sodium acid sulfate became moist within less than 3 days, tended to cake, and did not pour or move smoothly when stirred. The sodium acid sulfate-containing samples also rapidly and detrimentally attacked cardboard containers at elevated temperatures, e. g., 110 R, while the potassium pyrosulfate-containing mixtures did not appear to detrimentally attack such containers.

EXAMPLE 2 Single solution reducer Water cc 500 Potassium pyrosulfate grams 45 Ferric ammonium sulfate (crystals) (Ferric ammonium alum).- do- Water to make 1 liter.

The solid chemicals for preparing this reducer may be packaged in one compartment containing both the potassium pyrosulfate and ferric ammonium sulfate.

EXAMPLE: 3

Acid stop bath Grams Sodium acetate, anhydrous 20 Potassium pyrosulfate, powder (K2S2Q'7) 40 This dry chemical mixture is suitable for dissolving in Water to make 1 liter of solution.

EXAMPLE 4.

Preparation of acid stop bath using addition of dry packaged. potassium pyrosuljate Prepare a solution containing sodium acetate, anhydrous 20 grams in 1 liter of water. Add dry, packaged potassium bisulfate (pyro) fused, powder 40 grams to the sodium acetate solution; stir until dissolved and the solution is ready for use as a photographic acid short stop or stop bath.

EXAMPLE 5 Silver image bleach or tray cleaner Grams Potassium permanganate 4 Potassium pyrosulfate, powder 15 Y The dry ingredients packaged together are suitable for dissolving in water for the preparation of 1 liter of silver image bleaching solution or as a tray cleaner.

In packing where the solid potassium pyrosulfate is to be mixed with one or more solid substances and particularly when using water permeable containers, it is essential to avoid deliquescent compounds or compounds which are capable of forming crystalline hydrates that would subsequently react with the potassium pyrosulfate by double decomposition to give moist mixtures. In the case of moisture impermeable containers, it is desirable to avoid deliquescent compounds if the package is to be intermittently opened for use and also to avoid the use of hydrated substances such as certain crystalline hydrated sodium and lithium compounds the corresponding potassium compounds of whichare either anhydrous or form hydrates containing significantly lower relative molecular amount of water than the sodium and lithium compounds.

It will be understood that the examples included herein are illustrative only and that. my invention is to be taken as limited only by the scope of the appended claims.

.I claim:

1. A dry, packaged photographic composition adapted to form an acid hardening fixing bath when mixed in aqueous solution with'a fixing agent, a soluble sulfite, and a salt of an aliphatic acid containing two to four carbon atoms, which composition comprises approximately one part of potassium alum and approximately two parts of potassium pyrosulfate as the generator of free aliphatic acid by reaction with the salt thereof.

2. Photographic dry packaged compositions comprising approximately one part of; an alum and approximately two parts of potassium pyrosulfate for the preparation of photographicacid baths.

3. Photographic dry packaged compositions comprising a mixture of approximately one part of a salt of a weak organic acid and approximately two parts of potassium pyrosulfate for the preparation of photographic acid baths.

LOWELL E. MUEI-ILER.

REFERENCES CITED The following references are of'record in the file of this patent:

UNITED STATES PATENTS Name Date Russell et al June 12, 1945 Number 

1. A DRY, PACKAGED PHOTOGRAPHIC COMPOSITION ADAPTED TO FORM AN ACID HARDENING FIXING BATH WHEN MIXED IN AQUEOUS SOLUTION WITH A FIXING AGENT, A SOLUBLE SULFITE, AND A SALT OF AN ALIPHATIC ACID CONTAINING TWO TO FOUR CARBON ATOMS, WHICH COMPOSITION COMPRISES APPROXIMATELY ONE PART OF POTASSIUM ALUM AND APPROXIMATELY TWO PARTS OF POTASSIUM PYROSULFATE AS THE GENERATOR OF FREE ALIPHATIC ACID BY REACTION WITH THE SALT THEREOF. 